Thesis (M.Sc.) - Cairo University - Faculty of Science - Department of Microbiology

Bacterial wilt disease caused by Ralstonia solanacearum is a serious threat for agricultural production of tomato. In this study, 80 endophytic bacterial isolates were screened from healthy tomato plants in R. solanacearum-infested fields. Two endophytic antagonists designated HRA32 and HRA69, showing the highest antagonistic activity via in vitro screening, were identified as Pseudomonas fluorescens and Bacillus subtilis using 16S rRNA analysis. The selected isolates were evaluated, in vitro, for their activities related to plant nutrition and plant growth regulation. Both of the assessed endophytes were found to exhibit capabilities in ammonia, indoleacetic acid (IAA) and siderophore production as well as phosphate solubilization. Pot experiments were adopted to assess the growth promoting activity and control efficiency of selected endophytes against tomato bacterial wilt. Results revealed that isolates HRA32 and HRA69 significantly enhanced all measured growth criteria and yield increased by 23.8% over untreated control. Clear synergetic effect was observed in tomato plants treated with a mixture of the two antagonists by reducing disease incidence significantly from 87.22% in the control to 16.66% with biological control efficacy of 80.23%. Both endophytes were considered as elicitors that induced elevated levels of phenolic compounds and defence enzymes including phenylalanine ammonia lyase, peroxidase and polyphenol oxidase. It is concluded that application of P. fluorescens HRA32 and B. subtilis HRA69 may be a promising approach for improving tomato yield and controlling bacterial wilt disease and may play an important role in sustainable agriculture.

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